How to prevent exported bar graphs from having rounded corners

When you export bar graphs from Prism Windows in tiff (or most other formats), if you look closely, you'll see that the corners are rounded rather than sharp. You'll see this on the left graph below. The border is 5 points and the same color as the fill. The graph on the right has no border, and the corners are right angled. The rounded corners are subtle and barely noticeable with reasonable size borders (the 5 pt border below are quite thick). But if the rounded corner bothers you, the workaround is to use solid fills and to turn off the border. 

Prism file